1. Field of the Invention
The invention relates to a hybrid vehicle and a control method for a hybrid vehicle and, more particularly, to a hybrid vehicle that includes an internal combustion engine including a variable valve actuating device for changing the operation characteristic of an intake valve, and a control method for the hybrid vehicle.
2. Description of Related Art
In order to purify exhaust gas from an internal combustion engine, an exhaust emission control device including a catalyst is used. To cause the catalyst to sufficiently exercise a purification function, it is required to increase the temperature of the catalyst.
For example, Japanese Patent Application Publication No. 2012-40915 (JP 2012-40915 A) describes a hybrid vehicle in which catalyst warm-up control is executed. In the catalyst warm-up control, a catalyst of an exhaust emission control device is warmed up. In this hybrid vehicle, when warm-up of the catalyst is required, initially, an internal combustion engine is operated at a first operating point at which the ignition timing of the internal combustion engine is retarded, the ignition timing is returned after the temperature of a catalyst end has increased, and then the internal combustion engine is operated at a second operating point at which an output required of the internal combustion engine is fixed. When warm-up of the catalyst has completed, the internal combustion engine is shifted into ordinary operation in which the output required of the internal combustion engine is changed on the basis of an output required of the vehicle as a whole (see JP 2012-40915 A).
There is also known an internal combustion engine including a variable valve actuating device that is able to change the operation characteristic of an intake valve. There is also known a variable valve actuating device that is able to change at least one of the valve lift and valve operating angle of an intake valve as such a variable valve actuating device (see Japanese Patent Application Publication No. 2004-183610 (JP 2004-183610 A), Japanese Patent Application Publication No. 2013-53610 (JP 2013-53610 A), Japanese Patent Application Publication No. 2008-25550 (JP 2008-25550 A), Japanese Patent Application Publication No. 2012-117376 (JP2012-117376 A), Japanese Patent Application Publication No. 9-242519 (JP 9-242519 A), and the like).
The hybrid vehicle described in JP 2012-40915 A includes a generator that generates electric power by using the power of the internal combustion engine and that exchanges electric power with a secondary battery. When the internal combustion engine operates, the secondary battery is charged by the generator. The hybrid vehicle further includes an electric motor that generates a vehicle driving force by using electric power stored in the secondary battery.